This invention pertains to flowmeters of the electromagnetic type and in particular to high pressure electromagnetic flowmeters of the permanent magnet type. Such flowmeters include an electrically conductive duct for containing the flow of a conductive medium to be monitored. The duct is surrounded by a permanent magnet which creates a magnetic field perpendicular to the axis of the duct. The duct is formed of non-magnetic material so as not to distort the magnetic field which passes through the interior of the duct and the flowing conductive medium contained therein. As a conductive medium, such as liquid metal, is passed through the duct, an electromotive force (emf) is set up in a direction perpendicular to both the axis of the duct (i.e. the direction of medium flow) and the direction of the magnetic field passing through the flowing medium. The emf generated is proportional to the volumetric flow rate of the conductive medium as long as the velocity profile of the flow is axially symmetrical.
Frequently, such flowmeters must be installed in conduit sections subjected to great mechanical stress. One example of such stress occurs in a closed flow loop having a large temperature gradient throughout its length, i.e. an arrangement in which one section of the loop is operated at a much higher temperature than other sections. Depending primarily on the temperature difference in the loop and the type of materials used, large bending moments can be experienced in the cooler portions of the loop. Cooler portions of the loop are more suitable for electrical connections to the flowmeter location. Due to the mechanical stresses involved, the mass of the flowmeter must be significantly increased for greater mechanical strength in the direction of stress. However, if the increased mass must be located in the path of the induced emf output, significant reductions in the magnitude of the output signal, as well as the sensitivity of the flowmeter, result. Further complications arise if the flow loop is operated at high pressures, or if the flow loop contains a hazardous material which cannot be allowed to escape. In such cases, structural integrity of the flowmeter duct must be preserved so as to avoid the risk of hazardous material leakage.
One example of a flowmeter containing a hazardous material is found in a nuclear test reactor for testing fuel element containers which are cooled by liquid sodium. Such arrangements must provide fail-safe containment of the potentially radioactive coolant which contacts fuel element containers being tested for structural integrity under simulated operating conditions. Flowmeters placed in paths of coolant flow must not degrade the containment properties of the test reactor. Such degradation is particularly compromised when a sensitive flowmeter is subjected to the mechanical stresses of closed-loop liquid sodium systems.
It is therefore an object of the present invention to provide a magnetic flowmeter having increased sensitivity, which is capable of withstanding mechanical stress in a given direction, particularly the direction of induced emf.
It is another object of the present invention to provide an improved flowmeter of the above-described type having improved structural integrity providing an effective containment of high temperature, high pressure hazardous materials.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.